Field
The present disclosure generally relates to processes and systems for chemical cracking of hydrocarbons, and more specifically, to processes and systems for fluidized catalytic cracking of hydrocarbons incorporating series-reactor fluidized catalytic cracking units.
Technical Background
Crude oils are refined to produce transportation fuels and petrochemical feedstocks. Typically fuels for transportation are produced by processing and blending of distilled fractions from the crude to meet the particular end use specifications. After initial atmospheric and/or vacuum distillation, fractions are converted into products by various catalytic and non-catalytic processes. Catalytic processes are generally categorized based on the presence or absence of reaction hydrogen. Processes including hydrogen, often broadly referred to as hydroprocessing, include, for example, hydrotreating primarily for desulfurization and denitrification, and hydrocracking for conversion of heavier compounds into lighter compounds more suitable for certain product specifications. Catalytic conversion of hydrocarbons without the addition of hydrogen is another type of process for certain fractions. The most widely used processes of this type are commonly referred to as fluidized catalytic cracking (FCC) processes. A feedstock is introduced to the conversion zone typically operating in the range of from about 480° C. to about 550° C. with a circulating catalyst stream. This mode has the advantage of being performed at relatively low pressure, i.e., 50 psig or less.
In FCC processes, the feed is catalytically cracked over a fluidized catalyst bed. The main product from such processes has conventionally been gasoline, although other products are also produced in smaller quantities via FCC processes such as liquid petroleum gas and cracked gas oil. Coke deposited on the catalyst is burned off in a regeneration zone at relatively high temperatures in the presence of air before being recycled back to the reaction zone.